CESM recommends using the xmlchange tool to modify env variables. xmlchange
supports error checking as part of the implementation. Also, using xmlchange
will decrease the chance that typographical errors will creep into the
xml files. Conversion of the xml files to environment variables can fail
silently with certain xml format errors. To use xmlchange, do, for instance,

which will change the variables STOP_OPTION and STOP_N in the file env_run.xml
to the specified values.
The xml files can be edited manually, but users should take care not to
introduce any formatting errors that could lead to incomplete env settings.
See also .